The present invention relates to a developing apparatus for developing an electrostatic image, usable with an image forming apparatus such as a copying machine, a printer or the like of an electrophotographic type or an electrostatic recording type.
In developing means (developing apparatus) provided in the copying machine or printer, there is provided a sealing member for preventing leakage of the toner to outside of a developing zone at each end of a developer carrying member such as a rotatable developing roller of the developing apparatus. The sealing member for preventing the owner leakage is generally of felt, foam rubber or another elastic member.
The developing roller includes a magnet roller therein and is rotatably supported on a developing device frame through sleeve bearings. Therefore, the toner supplied from the developer container is deposited on the surface of the developing roller by the magnetic force of the magnet roller, and the thickness of a layer of the developer is regulated by a developing blade and is then fed to the developing zone where the developing roller is opposed to a latent image on the photosensitive drum by the rotation of the developing roller.
In addition, at a rear portion opposite from an opening side of the developing roller mounted to the developing device frame at each of the longitudinal ends of the developing roller outside the developing zone, an elastic sealing member is provided. The elastic sealing member is press-contacted to an outer surface of the developing roller to prevent leakage of the toner.
However, in the developing apparatus having such a structure, the elastic sealing member is press-contacted to one half of the outer surface of the developing roller, and therefore, the load of the developing roller against rotation thereof during the developing operation is large. By the contact to the developing roller, the elastic sealing member is deteriorated with results of insufficient sealing performance. Moreover, the toner, even if the amount thereof is small, enters between the developing roller and the elastic sealing member in some cases, with the result of increased torque or a large variation of the torque (non-uniform rotation). If this occurs, the image information is influenced.
In order to provide a solution to such problems, a proposal has been made to provide a magnetic sealing member (magnetic seal) with a predetermined gap at each end of the developing roller to prevent leakage of the toner.
The magnetic seal is made of a magnet, and is spaced from the outer surface of the developing roller with a predetermined gap (0.1-0.7 mm approx.) and wound around the developing roller. The magnetic sealing member is magnetized at the surface opposed to the developing roller to form a magnetic brush by the erected chains of toner particles along the magnetic lines of force. The magnetic brush fill the gap between the outer surface of the developing roller and the surface of the magnetic sealing member to prevent the toner from leaking out of the developing zone.
Since such a sealing method using the magnetic seal is based on the magnetic force the retain the toner in the gap between the magnetic sealing member and the surface of the developing roller, it is required to increase the magnetic flux density in the gap in order to enhance the sealing property. Particularly in the case that developing apparatus is of a cartridge type detachably mountable to the image forming apparatus, the toner leakage tends to occur due to vibration or shock upon the mounting and demounting operation thereof. Therefore, the magnetic force provided by the magnet for the magnetic seal has to be increased in such a case.
However, in the structure using the magnetic seal, a part of the toner in the gap between the magnetic seal and the surface of the developing roller comes out through the gap depositing on the surface of the developing roller by the rotation of the developing roller. By this, a toner layer is formed on the surface of the developing roller opposed to the photosensitive drum.
The toner is collected into an inlet portion of the gap by the further rotation of the developing roller, but if the magnetic flux density provided by the magnetic seal is high, the toner tends to stagnate at the inlet portion. With repetition of the developing operation, the amount of the stagnated toner gradually might increase even to such an extent that toner leaks to the outside of the developing apparatus.
In order to solve such a problem, U.S. Pat. Nos. 5,790,923 and 6,266,500 which have been assigned to the assignee of this application, proposes provision of a scraper for scraping the toner at the outlet of the gap between the magnetic seal and the surface of the developing roller to prevent the toner coming out through the gap between the magnetic seal and the surface of the developing roller from moving to the surface opposed to the photosensitive member.
However, in the case of apparatus in which the toner capacity is large in order to meet a large amount of prints, the amount of the toner scraped by the scraper with the result of gradually leaking out.
Accordingly, it is a principal object of the present invention to provide a developing apparatus capable of suppressing leakage of the developer.
It is another object of the present invention to provide a developing apparatus in which the developer stagnated in a space at the outlet of the magnetic sealing portions is effectively prevented from leaking out of the space.
According to an aspect of the present invention, there is provided a developing apparatus comprising a container, having an opening, for containing magnetic developer; a developer carrying member, rotatably disposed in the opening, for carrying the magnetic developer; a magnetic sealing member disposed spaced from a peripheral surface of said developer carrying member; and a removing member, disposed contacted to said developer carrying member, for removing the developer from the surface of said developer carrying member, said removing member being disposed adjacent an end, in a peripheral direction of said developer carrying member, of said magnetic sealing member; and a second sealing member for limiting movement of the developer from a space between said magnetic sealing member and said removing member toward a longitudinal end of said developer carrying member.
According to another aspect of the present invention, there is provided a developing apparatus comprising a container, having an opening, for containing magnetic developer; a developer carrying member, rotatably disposed in the opening, for carrying the magnetic developer; a magnetic sealing member disposed spaced from a peripheral surface of said developer carrying member; and a removing member, disposed contacted to said developer carrying member, for removing the developer from the surface of said developer carrying member, said removing member being disposed adjacent an end, in a peripheral direction of said developer carrying member, of said magnetic sealing member, wherein a surface facing the removing member and without facing to the peripheral surface of said developer carrying member of said magnetic sealing member includes two or more magnetic poles.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.